SOME SELF-HEATING CHARACTERISTICS OF VERY SMALL RESISTANCE STRAIN GAGES.
NAVAL POSTGRADUATE SCHOOL MONTEREY CALIF
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The self-heating of small foil resistance strain gages is studied both analytically and experimentally. The thermal resistance of the strain gage-specimen combination is obtained and utilized in relating the steady state temperature rise of the gage grid to the magnitude of the electrical current flowing through the gage. It is shown that the primary mechanism for dissipation of the gage self-heat is conduction through the gage backing, bonding adhesive, and specimen, then radiation and convection from the specimen surfaces to the environment. The heat dissipation paths provided by the lead wires and the exposed gage grid and tab surfaces are found to account for a negligible fraction of the heat transferred. For the smallest gages the backing and adhesive contribute nearly all of the thermal resistance of the primary path. In the latter cases it is shown that gage heating is substantially independent of the thermal conductivity or size of the specimen and that the gage power dissipation per unit grid area is the dominant parameter in predicting the steady-state temperature rise of the grid.